Module std::alloc

1.28.0 · source ·

Expand description

Memory allocation APIs.

In a given program, the standard library has one “global” memory allocator that is used for example by Box<T> and Vec<T>.

Currently the default global allocator is unspecified. Libraries, however, like cdylibs and staticlibs are guaranteed to use the System by default.

The `#[global_allocator]` attribute

This attribute allows configuring the choice of global allocator. You can use this to implement a completely custom global allocator to route all default allocation requests to a custom object.

use std::alloc::{GlobalAlloc, System, Layout};

struct MyAllocator;

unsafe impl GlobalAlloc for MyAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        System.alloc(layout)
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout)
    }
}

#[global_allocator]
static GLOBAL: MyAllocator = MyAllocator;

fn main() {
    // This `Vec` will allocate memory through `GLOBAL` above
    let mut v = Vec::new();
    v.push(1);
}

Run

The attribute is used on a static item whose type implements the GlobalAlloc trait. This type can be provided by an external library:

use jemallocator::Jemalloc;

#[global_allocator]
static GLOBAL: Jemalloc = Jemalloc;

fn main() {}

Run

The #[global_allocator] can only be used once in a crate or its recursive dependencies.

Structs

AllocErrorExperimental

The AllocError error indicates an allocation failure that may be due to resource exhaustion or to something wrong when combining the given input arguments with this allocator.

GlobalExperimental

The global memory allocator.

Layout

Layout of a block of memory.

LayoutError

The parameters given to Layout::from_size_align or some other Layout constructor do not satisfy its documented constraints.

System

The default memory allocator provided by the operating system.